Magnetic encoded credit cards are increasingly utilized in a variety of different transactions enabling a customer to charge the cost of goods and services purchased to an identified account. These cards, however, are expensive to write or encode due to the need for complex electrical circuitry for the card writers that are used for encoding the required data on the card. Some prior art magnetic card writers require precision drive mechanisms which propel the credit card past the record head. The use of such a precision drive mechanism is to ensure the writing of uniform bit spacing of an encoded data stream on the card so that the data can be synchronized with an internal clock source as it is retrieved from the magnetic card by a card reader.
To provide this synchronizing information on the magnetic card, other prior art writers encode a second row of timing information adjacent to the row containing the encoded data on the card. Thus, the data signal and the clock signal are both read by a card reader at the same time, thereby avoiding the use of an internal clock. Once again, however, the related circuitry is complex and expensive in the magnetic card writer and the associated card reader.
Some magnetic cards, moreover, are now encoded with self-clocking codes, such as the Aiken code, in which a signal containing both data and timing information is represented by a single bit stream. The signal is a binary signal of two-frequency coherent phase (bi-phase) encoding which combines serial data with clock information in that if a transition occurs between clock bits, the data is a "1" and if no transition occurs, the data is a "0". Card readers which use the width of the preceding bit as a basis for establishing an appropriate viewing window for the present bit can thereby read or decode this information on the magnetic card substantially independent of reading speed variations.
In a realization that card readers do not have to be precisely driven when a code such as the Aiken code is used, magnetic card writers have been developed that consider the insensitivity of these card readers to reading speed variations which also equate to an insensitivity to low frequency variations in the writing speed. These writers thus avoid the requirement for a precision drive mechanism in the writing of cards. Such writers are disclosed in U.S. Pat. No. 3,708,748, issued to E. G. Nassimbene on Jan. 2, 1973, and U.S. Pat. No. 3,597,752, issued to C. Eldert et al. on Aug. 3, 1971.
In order to write cards manually, however, a means must be provided to assure that the data will all be recorded on the card and reasonably dispersed thereupon. Since different individuals will move a card through the card writer at different rates, some means must be provided to determine this movement rate and then adjust the writing rate to the individual using the card writer. It is, therefore, desirable to provide a simple and inexpensive rate adaptive card writer which, when using the Aiken or other similar self-clocking code, will allow the writing of magnetic cards that can be read by single head rate adaptive readers.